The present invention relates to a magnetic separator, which can more particularly used for the separation or cleaning of particles having different magnetic properties.
Such a magnetic separating, sorting or classifying device is constituted by a treatment space immersed in a magnetic field, whose characteristics make it possible to selectively act on substances having different magnetic susceptibilities. The particles treated are subject to different forces, namely a magnetic force linked with the magnetic properties of the substance and forces which are independent of the magnetic properties of the substance, mainly gravitational forces, together with the resistance forces due to viscosity.
It is known that the deflecting effect on a magnetic field of particles having magnetic properties is proportional to the product of this magnetic field by its gradient.
French Pat. No. 2 253 567 describes a magnetic separation process for weakly magnetized particles. This process essentially consists of using a multipole field in the separation space on which is superimposed a substantially homogeneous magnetic field (p. 3, line 5 ff.). More specifically, in the example described (p. 5, line 29 ff.) the divided magnetic field is a quadripole field, on which is superimposed a homogeneous magnetic field produced by a solenoid in the longitudinal direction of the quadripole. The additional feature of the solenoid is in this case perpendicular to the field of the quadripole. Theory, calculation and experience show that in this case the accelerations in the three directions of the space are unchanged, i.e. the gain on the separating power is zero.
In the publication by E. C. Hise, A. S. Holman and F. J. Friedlaender: "Development of high-gradient and open-gradient magnet separation of dry fine coal" in IEEE TRANSACTIONS ON MAGNETICS, vol. 17, no. 6, November 1981, pp. 3314-3316, magnetic separation based on the following method is described.
Particles to be separated fall freely into a volume where an adequate magnetic field is applied. The magnetic field is chosen in such a way that at the end of the fall, the particles having different magnetic susceptibility are collected at different points.
The magnetic separator according to the aforementioned article comprises a stack of coils having a symmetry of revolution. In this configuration, the horizontal component of the separating force is cancelled out on the central axis of this separation space and which is surrounded by coils. When the particle beam to be separated falls in the vicinity of said central axis, the separation in this substantially zero field is mediocre.